The present invention relates generally to semiconductor fabrication processes, and more specifically, to a method of selectively forming a barrier layer on a substrate.
Substrates including metallic electrical interconnects are typically formed using a wide variety of etching techniques to selectively form and locate targeted layers, such as barrier layers, on the substrate. In many cases, it is desirable to etch a targeted layer without damaging one or more layers formed beneath the targeted layer. Planarization techniques, such as a chemical-mechanical planarization (CMP) process, are typically used to remove one or more metal layers. The CMP process, however, provides poor metal selectivity and can inadvertently damage soft polymeric dielectric films that are intended to be preserved.
Chemical etching techniques are also used to remove targeted layers formed on a semiconductor substrate. However, the effectiveness of conventional chemical etching techniques is limited to the particular material of the targeted layer. Chemical etching techniques also cause undesirable undercutting in the etched layers.
Laser etching techniques, such as ablative photodecomposition (APD), are based on a concept that energy can be imparted to a substrate using a laser radiation to selectively ablate a targeted layer. Radiation absorption occurs very rapidly and produces material fragments which eject or “ablate” from the surface of the material, leaving behind a localized etched region. Selectivity can be provided using a mask to limit where laser radiation is applied to a targeted layer, or through the inclusion of features in the target layer which have different ablation thresholds. The manner in which material is removed by APD is related to the amount of laser radiation applied and properties of the features including its vaporization temperature, radiation absorption, and thermal conductivity. This process can work in such a manner in which laser radiation sufficiently heats or shocks the metal due to discontinuity of the interface, a specified feature or area such that nearby features, with lower thresholds, experience APD, possibly in a manner which ejects the initially radiated feature.